Comparison of Ultrasound and Computed Tomography Scanning Accuracy in Diagnosing Acute Appendicitis at King Abdulaziz University Hospital

Background: Choosing the most effective and accurate preoperative modality is one of the most significant tools in the clinical diagnosis of acute appendicitis (AA) to prevent negative appendectomies, diagnosis confusion, and delayed treatment. This decision making remains challenging to emergency physicians and surgeons which lead this study to determine the sensitivity and specificity of ultrasound (US) and computed tomography (CT) in predicting AA using pathology reports as a reference at King Abdulaziz University Hospital (KAUH), Jeddah, Saudi Arabia. Methods: This study was conducted retrospectively at the Emergency Department, KAUH in Jeddah, Saudi, Arabia using 351 medical records with a clinical picture of acute appendicitis and no history of trauma. The sensitivity and specificity were calculated for ultrasound and computed tomography imaging. The positive predictive values (PPV) and negative predictive value (NPV) were also evaluated. Results: Out of the total 351 patients included in this study, 83 patients underwent surgical appendectomies and the pathology results revealed that 64 patients were diagnosed with AA while 19 showed a normal appendix. Of the 64 patients, 18 underwent US imaging while 62 underwent CT imaging. Compared to pathology results, US imaging results revealed that 12 out of 14 positive patients (85.7%) and only two out of four negative patients (50.0%) were correctly predicted while two out of 14 positive patients (14.3%) and two out of four negative patients (50.0%) were falsely diagnosed. On the other hand, CT imaging results revealed that 46 out of 49 positive patients (93.9%) and 9 out of 13 negative patients (69.2%) were correctly predicted while only three out of 49 positive patients (6.1%) and only four out of 13 negative patients (30.8%) were incorrectly diagnosed. Conclusion: Having an accuracy of 88.71%, sensitivity of 92.00%, and specificity of 75.00%, CT imaging was found to be more effective and accurate than US imaging which was only 77.78% accurate, 85.71% sensitive, and 50.00% specific. Statistical analyses also revealed that US results have a significant difference with pathology results (P= 0.130) while CT result has no significant difference (P <0.001).


Introduction
Appendicitis refers to the inflammation in the vermiform of the appendix [1]. Globally, it was estimated that there are 11 cases of acute appendicitis (AA) in every 10,000 population per annum [2]. In almost every emergency department, AA has been considered as the most prevalent cause of pain in the lower abdominal part of a suspected patient. In a general population, the overall risk and prevalence for AA is approximately 7% wherein it was estimated that the risk for males and females are 9% and 6%, respectively. Considering the available data for geographical differences, it was estimated that the lifetime risks for the USA, Europe, and Africa are 9%, 8%, and 2%, respectively [2][3][4][5]. Moreover, AA is believed to occur at any age but rarely occurs at extreme ages. Approximately, AA peak prevalence occurs between the age of 10 to 14 years for female patients while the age of 15 to 19 years for male patients [2,3].
For the past decades, appendectomy has been considered one of the most extensively performed types of treatment for appendicitis. Although it is generally tolerated, such surgical operation is still associated with postoperative morbidity and mortality [2]. Thus, it is very fundamental to achieve high accuracy in clinical diagnosis in order to provide better decision making as to whether appendectomy is necessary for a suspected patient or not [4]. The clinical diagnosis of AA can be done through the patient's historical record, physical examinations, and laboratory tests. For patients with typical signs and symptoms, the diagnosis might be straightforward, but the presentation is often atypical which might lead to diagnosis confusion and treatment delay [3,6]. For some instances where the clinical diagnosis is questionable, preoperative imaging, 1 1 1 namely US, CT, and magnetic resonance imaging (MRI), should be used [7]. For the past years, the US has been used as an important tool in diagnosing AA among suspected patients and as a basis for a clinical examination continuation [7]. Meanwhile, CT has been significant in decreasing the percentage of unnecessary appendectomies and was accepted as the standard for the evaluation of patients with suspected AA. Lastly, MRI has shown a high accuracy rate in AA detection and usefulness during the inapplicability of radiation, such as for pregnant women and young patients [8].
In this study, the effectiveness of CT and US in predicting AA at KAUH was evaluated. Specifically, it aimed to compare the sensitivity and specificity of the two radiological tests in predicting AA and compared their reliability against the pathology results of accurately diagnosed AA patients.

Study subjects and design
This study was conducted retrospectively at the Emergency Department, KAUH in Jeddah, Saudi, Arabia using 351 medical records with a clinical picture of acute appendicitis with no history of trauma. The most commonly observed clinical presentations included acute right iliac fossa pain, vomiting, nausea, positive sonographic murphys' sign and/or rebound tenderness. None of the collected data from this study can be associated with the patients' personal identities. No personal identifier was used during the data collection and analysis. All patients were admitted between January 2016 and January 2019 and diagnosed with AA, regardless of their demographic data, such as age and gender. The total population comprised 127 males (36.2%) and 224 females (63.8%), with a mean age of 32.09 ± 17.3, minimum and maximum age of 4 and 83 years old, respectively. Two independent authors collected the data from the hospital's electronic medical records and radiology Picture Archiving and Communication Systems (PACS), evaluated for inclusion/exclusion criteria, and performed the analyses. Inclusion criteria were comprised of the suspected clinical picture of acute appendicitis who underwent either ultrasound imaging, computed imaging, or both, without an alternative diagnosis at discharge. Patients with alternative diagnoses based on imaging or histopathology, perforation on imaging, or treated as perforated acute appendicitis were excluded from the study. Histopathological results on tissue obtained from appendectomy were used as the standard for the final diagnosis of AA and for the evaluation of the effectiveness of US and CT scanning in determining AA. The sensitivity and specificity were calculated for both imaging techniques. The positive predictive values (PPV) and negative predictive value (NPV) were also evaluated. Meta-analyses were performed for relevant subgroups, and sensitivity analysis was completed to account for outliers.

Statistical methodology
This study was analyzed using SPSS version 23 (IBM Corp., Armonk, NY). A simple descriptive statistic was used to define the characteristics of the study variables through the form of counts and percentages for the categorical and nominal variables while continuous variables are presented by mean and standard deviations. All relevant parameters such as the accuracy, sensitivity, specificity, PPV, NPV, and disease prevalence are expressed as percentages. The confidence intervals (CI) for accuracy, sensitivity, and specificity were reported as "exact" Clopper-Pearson CI.

Results
Female predominance at 63.8% was observed in the total population of included patients' medical records (n= 351), giving only 36.2% for male distribution. The total population was classified according to four age groups. The mean age was 32.09 ± 17.3 years old with a minimum age of 4 and maximum age of 83. The data are shown in Table 1.

CT: Computed Tomography
Using the number of patients with surgical-pathological confirmed acute appendicitis, the diagnostic accuracies of using US and CT imaging were compared to the obtained pathology results (

Discussion
Acute appendicitis, produced via appendix inflammation, has been considered as the most common etiological factor for abdominal pain with a lifetime prevalence of 7%. Despite its prevalence, clinical diagnosis of AA remains challenging and needs the importance of imaging modalities in the detection of AA among suspected patients. However, the decision to choose which diagnosing technique should be used remains challenging [4]. US imaging is widely used as the basic diagnostic technique and is usually the continuation of the clinical examinations for suspected AA patients. It is considered a more viable choice for children but usually gave an indistinct result for older patients. Some studies also revealed that there was a significant difference in the US results of obese and non-obese patients due to the interferences caused by an extreme proportion of extra-mesenteric fats [9]. From these, CT imaging is considered as a more applicable choice to some patients like obese and older individuals in which US imaging is not that clear. Its higher sensitivity, which approaches 100%, is clearly an advantage but its costs and the ionizing radiation exposure are some of its drawbacks [4,7]. With an estimated risk of 2%, the exposure to radiation that may induce cancer was addressed by introducing MRI as an alternative technique that can also give high accuracy in determining AA [10][11][12]. Considering several factors, such as accuracy, availability, and safety, any of these imaging techniques may be used to avoid delay in the diagnosis of AA [13]. Nonetheless, CT has been used as the reference standard, on top of US and MRI, for determining appendicitis since the start of the millennium [7,12].
The diagnostic accuracies of both US and CT imaging in diagnosing AA were compared. The US accuracy was 77.78%, sensitivity was 85.71% and specificity was 50.00%. Similarly, Farooq and co-workers (2020) reported a comparable US accuracy of 77.5%, sensitivity of 80%, and specificity of 60% [14]. Ahmed and co-workers (2016) also demonstrated comparable findings with a US accuracy of 84%, sensitivity of 86%, and specificity of 80% [10]. On the other hand, Alelyani and co-workers (2021) reported some inconsistent trends in which the US accuracy and sensitivity are relatively lower at 46.2% and 38.9%, respectively, but with a specificity of 89.5% [15].
Comparing US to CT imaging, this study showed better performance for CT imaging which was 88.71% accurate, 92.00% sensitive, and 75.00% specific. The PPV and NPV of US imaging were also lower than that of CT imaging. The respective values were 85.71% and 50.00% for US imaging while 93.88% and 69.23% for CT imaging. These findings were in line with the results obtained by Hwang (2018) as the diagnostic pooled values for sensitivity, specificity, PPV, and NPV in US imaging were 86%, 94%, 100%, and 92%, respectively. Meanwhile, the respective values for CT imaging were 95%, 94%, 95%, and 99% [16]. Consequently, Alshebromi and co-workers (2019) reported that US imaging has a sensitivity of 37.0% and specificity of 100.0% while CT imaging has 86.0% and 16.7%, respectively [8]. Reich and co-workers (2011) also compared US and CT imaging in terms of sensitivity and PPV in which results revealed that CT had better sensitivity and PPV of both 100% compared to that of US with sensitivity and PPV of 68.4% and 94.5%, respectively. The negative appendectomy rate (NAR) was also compared, and a significant difference was seen between the 0% NAR of CT imaging and 5.5% of US imaging, reported after positive imaging [17]. Another study that demonstrated the effect of BMI on the accuracy of US and CT in diagnosing appendicitis in children also revealed that CT has better sensitivity of 96% and specificity of 97% compared to that of US with an overall sensitivity of 38% and a comparable specificity of 97%. It was also observed that CT gave excellent accuracy regardless of BMI while US has a decreasing sensitivity with an increasing BMI [6]. The same findings regarding the accuracy of the two were also obtained by van Randen and co-workers (2011) in which the sensitivity of CT was higher at 94% compared to the 76% sensitivity of US imaging [18]. Another prospective study also directly compared the two and the results agreed that CT was superior to US. The obtained CT sensitivity was 100% and specificity was 100%, while the US sensitivity was 91% and specificity was 98% only [19]. A systematic review, conducted by Karul and co-workers (2014), revealed that US imaging also had lower sensitivity and specificity than CT imaging, in general. For US imaging, the pooled sensitivity and specificity values ranged from 71.2-92.0% and 83.3-96.6%, respectively. For CT imaging, the respective pooled values ranged from 89.0-100.0% and 89.0-98.0% [7].
Despite the alignment with the related literature, US imaging has still been extensively used even if its accuracy in diagnosing AA was not high compared to CT imaging. Its non-invasiveness and costeffectiveness have been its principal advantage against the latter. However, the consistent quality examination and reproducibility of CT scanning can provide a more accurate diagnosis, which may lower diagnosis confusion, delay treatment, and even mortality. With these, it is recommended that inconclusive US imaging results should be verified via CT imaging [5,7].

Limitations
This study has potential limitations to be considered. First, the body-mass-index (BMI) of the patients was not studied. It is well known that US has the difficulty in penetrating the fat; thus, the US imaging results might be equivocal for obese patients, in case there is any. Second, the sensitivity of US imaging might vary and might be underestimated depending on the sonographer who administered the results. Being used for initial and urgent diagnosis, US is usually performed and interpreted by an unsupervised radiological resident rather than an attending radiologist. In some literature, it was found that US results performed by an unsupervised resident gave a significantly lower sensitivity than that interpreted by an attending radiologist [20]. Lastly, the age bracket of <20 years old was a wide range and may partially contribute to an adult population; thus, the study cannot be generalized to children.